Automatic production lines are known where the workpieces are arranged on workpiece carriers, known in the field as pallets and hereinafter thus indicated, which hold them and carry them through one or several workstations. An example of workpieces is an armature for an electric motor.
More precisely, each pallet, that is initially located in a station of inlet for receiving a workpiece, proceeds on a conveyor belt that causes it to move selectively through the workstations. In each station, if necessary, the workpiece is offered to a machine that draws it from the pallet, works it and returns it again on the pallet that proceeds on the conveyor. During the working time of the workpiece in a station, the pallet continues to rest on the conveyor belt located underneath, for example of the belt type, in sliding contact on the belt same, or it can be raised or withdrawn from the conveyor belt, for example put in a waiting station. At the end of the work cycle, the pallet is withdrawn or maintained on the conveyor belt because it can proceed up to a next workstation.
Alternatively to the above, the workpiece can be worked directly on the pallet, which is being kept still on the conveyor belt or, as above described, raised or withdrawn from the latter.
Production lines that are not flexible exist, i.e, prepared to operate on workpieces having all the same size or workpiece families of substantially alike size. In this case, at the start-up of the line the pallets are set for receiving the workpieces and are not modified up to the end of all the working period. When the size of the workpieces is modified in a substantial way, the line is stopped and both the pallet and the machines are set for receiving and working the new workpieces.
When, instead, the machines in the various stations of the line are of flexible type, i.e., they can be adapted quickly to operate with workpieces of different size, also the pallet, therefore, must be adjusted in real time not much before receiving each workpiece.
Manually adjustable pallets exist, like in EP267324, that comprise fixed supports that can be adjusted and then blocked in a precise position for receiving the workpiece. A pallet manually adjustable of traditional type, requires that the supports are loosened, for example by means of screw coupling, in order to move them to a position in which they are then are locked to steadily support the workpiece.
Pallets with automatically adjustable supports are also known. For example, in EP 348715 a pallet is described for armatures of electric motors having a couple of V-supports that receive the shaft ends of the armature. The V-supports are mounted by means of sliding coupling on guides integral to the pallet. Means are provided for moving the supports along the guide, such as a worm screw, that can be operated automatically in many ways in an adjustment station. In all the various embodiments presented, however, the pallet is structurally complex and heavy to make, and requires complex means for adjusting.
In IT 5107/A/89 a similar pallet is described for armatures of electric motors with variable distance support members along with the relative means for adjusting.
In EP 447805 a pallet is shown for armatures of electric motors having a much easier substantially frame-shaped structure defining a central aperture. On the frame a T-guide is mounted with which support arms slidingly engage having a V-shaped end for receiving the workpiece.
In EP 811463, finally, a pallet is described for armatures of electric motors with supports adjustable both manually, made quickly by an operator, and automatically by a robotized manipulation device. In fact, in the case of production lines of small and medium size, an automatic adjustment station of the distance between the supports may be not necessary, whereas on very flexible lines it can be required.
EP 811463, however, provides cantilever support arms mounted on a support bar, whereby the armatures bear with all their weight on the fastening ends of the arms to the bar. Also EP 348715 and EP 447805 have cantilever supports with respect to a guide, whereby the moment of the weight of the armature bears on the guide.